The first cauliflower ear of maize was reported by Collins (Smithsonian Inst. Report Plate 25, 1937). It was a result of combining homozygous ramosa (ra ra) with heterozygous full tunicate (Tu tu) in a family segregating these two genes. The combined phenotype of these two genes is a cauliflower ear monster incapable of propagation except as a recombinant in a segregation. But now, 50 years after its first appearance, this monster has returned with renewed hope for a successful role in macroevolution.

Since the early observations of Collins, mutations to intermediate tunicate alleles (tu-l and tu-d) have been discovered by Mangelsdorf (Mangelsdorf and Galinat, P.N.A.S. 51:147-150, 1964), and in contrast with full tunicate, these weaker alleles may be propagated as homozygotes. We have produced the double homozygote (tu-l tu-l, ra ra) and have found that its phenotype is identical to that observed by Collins (1937) for homozygous ramosa with heterozygous full tunicate. That is, both are cauliflower sterile as a lateral ear in a background of modern dent corn. Apparently, an incongruous combination of genetic instructions causes the female flowers to abort in a parallelism to a head of cauliflower. Under internal conditions at a lowered level on the plant that cause the pistil to become extremely precocious, the combination of the tunicate (long glume) gene that further increases female earliness with the ramosa gene that puts developmental priority on a branching of the rachis results in an inadequacy by the supply system to function soon enough to nurture its spikelets. But in a different position on the same plant where pistil development is less precocious, such as the inflorescences of long tillers, the relational balance may be improved, female fertility normal and the way opened to successful macroevolution. The tassels of tunicate ramosa have normal male fertility.

Walton C. Galinat
 
 

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